A. Sexual Dysfunction
Impotence or erectile insufficiency is a widespread disorder that is thought to affect about twelve percent of adult men under age forty-five, about twenty percent of men at age sixty, and about fifty-five percent of men at age seventy-five.
There is more than one cause of erectile dysfunction. For example, erectile dysfunction can be psychological, resulting from anxiety or depression, with no apparent somatic or organic impairment. Such erectile dysfunction, which is referred to as “psychogenic,” is responsible for about fifteen to twenty percent of cases of impotence. In other cases, the erectile dysfunction is associated with atherosclerosis of the arteries supplying blood to the penis; such dysfunction is referred to as “arteriogenic” or “atherosclerotic.” About forty to sixty percent of cases of impotence are arteriogenic in origin.
In still other cases, there is leakage from veins in the penis such that sufficient pressure for an erection can be neither obtained nor maintained. This dysfunction is referred to as “venous leakage,” or “abnormal drainage.” This condition is often exacerbated by the presence of some arteriogenic dysfunction whereby the supply of blood to the penis is impaired. In still other cases, the dysfunction is associated with a neuropathy, such as nerve damage arising from, for example, surgery or a pelvic injury, in the nervous system affecting the penis. Such a dysfunction is referred to as “neurogenic” and this accounts for about ten to fifteen percent of cases of impotence.
There is also a high incidence of erectile insufficiency among diabetics, particularly those with insulin-dependent diabetes mellitus. Erectile dysfunction in diabetics is often classified as “diabetogenic,” although the underlying dysfunction is usually neurogenic associated with neuropathy, but may be arteriogenic or neurogenic and arteriogenic. About half of diabetic males suffer from erectile insufficiency, and about half of the cases of neurogenic impotence are in diabetics.
Additionally, erectile insufficiency is sometimes a side effect of certain drugs, such as beta-blockers that are administered to reduce blood pressure in persons suffering from hypertension, or drugs administered to treat depression or anxiety. Excessive alcohol consumption has also been linked to erectile insufficiency. Circumcision in males, which removes highly sensitive penile tissue (Cold, C. J. and Taylor, J. R., “The Prepuce” British Journal of Urology, 83, Suppl. 1:34-44, 1999) and subjects the glans and shaft of the penis to desensitization through keratinization of the remaining tissue, is also believed to be a contributing factor to some forms of erectile insufficiency (Fink K S, Carson C C, DeVellis R F. “Adult circumcision outcomes study: effect on erectile function, penile sensitivity, sexual activity and satisfaction” J Urol, 167:2113-6, 2002). Additionally, one cause of erectile insufficiency may act synergistically with one or more other causes of erectile insufficiency. In this regard, routine infant circumcision may be a latent causative factor in all instances of erectile insufficiency in circumcised males.
A number of methods to treat impotence are available. These treatments include pharmacological treatments, surgery and, in cases of psychogenic dysfunction, psychological counseling is sometimes effective. Psychogenic impotence often can be cured by counseling coupled with a demonstration to the patient that he is capable of having a full erection by inducing such an erection once or a few times in the patients. Insufficiency due to excessive alcohol consumption is sometimes cured by reducing or elimination such consumption.
In rare cases, where the insufficiency is physical because of venous leakage, surgery can usually be employed to repair the venous lesion and thereby either cure the insufficiency or, if there remains an erectile insufficiency after repair of the venous lesion, render the insufficiency amenable to treatment by pharmacological methods. Also, penile implants, which provide a mechanical means to produce an erection sufficient for vaginal penetration, are widely used to treat impotence. In recent years, implants have been employed, especially in cases where pharmacological intervention is ineffective, which are usually cases of severe atherogenic impotence. Treatment of impotence with penile implants, however, entails serious disadvantages. Such treatment requires surgery and necessitates total destruction of the erectile tissues of the penis, forever precluding normal erection.
Pharmacological methods of treatment are also available. Such methods, however, have not proven to be highly satisfactory and can be accompanied by severe side-effects. Papaverine is now widely used to treat impotence, although papaverine is ineffective in overcoming impotence due, at least in part, to severe atherosclerosis. Papaverine is effective in cases where the dysfunction is psychogenic or neurogenic and severe atherosclerosis is not involved. Injection of papaverine, a smooth muscle relaxant, or phenoxybenzamine, a non-specific blocker and hypotensive, into a corpus cavernosum has been found to cause an erection sufficient for vaginal penetration. Also, in cases where severe atherosclerosis is not a cause of the dysfunction, intracavernosal injection of phentolamine, an α-adrenergic blocker, causes an erection sufficient for vaginal penetration. The resulting erection is one of significantly shorter duration than that induced by intracavernosal injection of papaverine or phenoxybenzamine and is of such short duration that satisfactory sexual relations are difficult or impossible.
Treatment of impotence with papaverine or phenoxybenzamine often results in priapism, a locking-up of an erection for a long period of time, typically a few hours and sometimes longer than twenty-four hours. Priapism is a serious, deleterious side effect of treatment of erectile insufficiency with these drugs. Beyond the embarrassment that may be caused for some men, priapism is usually painful, irreversibly damages erectile tissue, and, to be relieved, requires bleeding or pharmacological intervention, such as injection of a sympathomimetic drug, such as adrenaline.
Even if priapism does not occur with use of papaverine, such use is associated with a painful, burning sensation in the first two or so minutes after the injection and there are indications that repeated use of papaverine causes undesirable, extensive intracavernous fibrosis. Further, as indicated above, impotence arising from severe atherosclerosis is not susceptible to treatment with papaverine, phenoxybenzamine, phentolamine or papaverine together with phentolamine. In any case, phenoxybenzamine is not suitable for use in treating impotence because it is a carcinogen.
Sildenafil citrate (Viagra) has also been utilized as a pharmacological treatment for impotence. However, sildenafil citrate has a lack of specificity for its target, enzyme phosphodiesterase 5 (PDE5), and exerts a definite inhibition on the enzyme phosphodiesterase 6 (PDE6), located in the retina. It has been shown that the inhibition of PDE6 results in color vision defects as a side effect of treatment with sildenafil citrate. Furthermore, side effects such as flushing, headache, nasal congestion, and dyspepsia (heartburn) have also been associated with sildenafil citrate treatment of impotence. (See, Moreira et al., “Side-effect profile of sildenafil citrate (Viagra) in clinical practice,” Urology, 56(3): 474-76 (2000)).
Females have sexual dysfunction. Post-menopausal women often complain of discomfort with intercourse, dryness of the vagina and diminished vaginal arousal. Studies comparing sexual dysfunction in couples have revealed 40% of the men had erectile or ejaculatory dysfunction whereas 63% of the women had arousal or orgasmic dysfunctions. Similar to male sexual dysfunction, the prevalence of female sexual dysfunction has been shown to increase with age and be associated with the presence of vascular risk factors and the development of the menopause.
The clitoris is the homologue of the penis. It is a cylindrical, erectile organ composed of the glans, corporal body and the crura. The corporal body is surrounded by a fibrous sheath, tunica albuginea, which encases cavernosal tissue consisting of sinusoids and surrounding smooth muscle. The clitoris responds to sexual excitement by tumescence and erection, although this does not occur with the degree of pressure elevation as found during penile erection. The characteristics of the clitoral blood flow, however, approximately parallel those of the male. See K. Park et al., “Vasculogenic female sexual dysfunction: The hemodynamic basis for vaginal engorgement insufficiency and clitoral erectile insufficiency,” Int. J. Impotence Res. 9:27 (1997).
Post-menopausal women and women with a history of vascular risk factors have been shown to have significantly more complaints of self-reported female vaginal and clitoral dysfunctions than pre-menopausal women or women without vascular risk factors. Such problems include, but are not limited to, atherosclerosis-induced vaginal engorgement insufficiency and clitoral erectile insufficiency syndromes.
B. Cardiovascular Disease
Cardiovascular disease is the number one cause of death in the United States. Medical Sciences Bulletin, No. 238; p. 1 (1997). While cardiovascular disease presents many different clinical manifestations, hypertension and congestive heart failure (CHF) are major components of this disease state. Uncontrolled hypertension can result in myocardial infarction and stroke. Congestive heart failure, if untreated, is an ultimately fatal disease that kills more than half its victims within five years of initial diagnosis. CHF affects about 3 million people in the United States and about 15 million worldwide. Currently, an estimated 400,000 new cases are diagnosed in the United States each year, and CHF is responsible for about 900,000 hospitalizations a year.
The current treatment approaches involve anti-hypertensive compounds, such as: beta-blockers, calcium channel blockers (especially dihydropyrimidines), angiotensin-converting enzyme (ACE) inhibitors, diuretics, and alpha-blockers. However, many patients fail to respond to (or tolerate poorly) these compounds.
For example, many patients do not respond to diuretics (with or without digitalis). Moreover, many patients cannot tolerate (or respond poorly to) ACE inhibitors. In addition the use of beta blockers has been associated with loss of glycemic control. Studies on the Glycemic and Lipidemic Effect of Atenolol and Propranolol in Normal and Diabetic Rats, (Abstract), Arzneimittelforschung, 44(4): 496-501 (April, 1994).
What is needed is a pharmaceutical that is effective in the treatment of sexual dysfunction in males and females but lacking in significant side effects. Additionally, what is needed is a pharmacological intervention for cardiovascular disease [including, but limited to, hypertension and congestive heart failure (also referred to as “CHF”) that is less disruptive to the patient and is be better tolerated in comparison to existing treatment modalities.